1. Field of the Invention
The present invention relates to light-emitting devices, and more particularly, to an alternating current light-emitting device and a fabrication method thereof.
2. Description of the Prior Art
With continual advances in optoelectronic technology, light emitting diodes (LED), a kind of light sources, are in wide use and of vital importance to optoelectronic industry. In an AC-dominant living environment, conventional DC-driven LED chips can function well only in the presence of an external AC-to-DC converter circuit and a voltage drop element, thus resulting in high costs and unsatisfactory performance. This problem calls for development of AC-operated LED chips. AC-operated LED chips (AC LED) have been put forth by manufacturers based in the United States, Japan, South Korea and China since 2005, indicating that AC LED is deemed a novel component of great potential.
U.S. Pat. Nos. 6,547,249 and 6,957,899 and Taiwanese Patent Application No. 093126201 disclose a single chip having a plurality of miniaturized light-emitting diode dies connected to one another such that the chip is directly operated in a high-voltage AC environment, and the disclosures share features as follows: at least one AC microdie LED module formed on a chip, wherein the AC microdie LED module at least comprises two LED microdies electrically connected to one another, and under an applied alternating current the microdies emit light in turn in accordance with the way of circuit connection. Although the LED microdies function very well in an AC environment, each of the LED microdies emits light during half of a cycle. This means a waste of light-emitting area, as only half of the microdies are operating at a forward bias at every single instant in an AC environment.
To overcome the aforesaid drawback, a design of AC LED with an equivalent circuit like Wheaston's bridge was put forth, which involves disposing a light-emitting microdie module in a region of constant direction of rectified current to allow the light-emitting microdie to emit light whether the AC bias is forward or reverse. However, the design brought about another problem: LEDs have poor tolerance to a reverse bias, and thus rectification can only be achieved by LEDs when a large number of LEDs are used, which also results in a waste of microdie surface area.
Accordingly, the aforesaid drawbacks of the prior art call for immediate solution for directly fabricating on the surface of a LED die a rectifying element highly tolerant of reverse bias and characterized by low starting forward bias.